1. Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board. Particularly, the present invention relates to a method for manufacturing a packaging type multi-layer printed circuit board, in which in a multi-layer printed circuit having a window region for installing a semiconductor chip, when a metal is plated on an upper board to form a circuit, bonding fingers for being bonded with the semiconductor chip are prevented from being electroplated with a metal.
2. Description of the Prior Art
Recently, according as the high density integrated circuit chips are made to have a high speed and a high function, the circuit board for installing the semiconductor chips has to have a high speed and a high function. Therefore, for the sake of a high speed and a high function, packaging type circuit boards (to directly install the semiconductor chips) are being proposed. Among these packaging type circuit boards, the chip-on-board type circuit board consisting of a plurality of can form a particularly high density circuit, and therefore, this board is calling for a particular attention.
FIG. 1 illustrates a conventional packaging type multi-layer printed circuit board for installing semiconductor chips. As shown in this drawing, this printed circuit board consists of a plurality of, with circuits formed thereon. Except a first copper clad lamina 1a which forms the bottom of the circuit board, other 1b, 1c and 1d form a window 4 into which a semiconductor chip 7 is to be installed.
In the above described printed circuit board, there are used both-side copper clad laminates(CCL). Accordingly, the copper cladding of the both faces of the CCLs 1a, 1b, 1c and 1d are etched to form circuits. Further, the CCLs 1a, 1b, 1c and 1d are coupled together by adhesive layers 2a, 2b and 2c which consist of prepreg. The CCLs 1a, 1b, 1c and 1d are different in their lengths. That is, the window for installing the semiconductor chip is different in its width at different CCLs, and therefore, when the CCLs 1a, 1b, 1c and 1d are coupled together, the window is formed in a multi-step shape.
Generally, the above described multi-layer printed circuit board is manufactured in the following manner. That is, the respective CCLs 1a, 1c, 1c and 1d are prepaid separately, and window regions are formed. Then the CCLs are coupled together by using the prepreg. Therefore, if the window 4 as shown in the drawings is to be formed, the window regions of the respective CCLs have to have different sizes.
In this manner, the window 4 is formed in a multi-step shape. Accordingly, parts of the second CCL 1b and the third CCL 1c are exposed to the outside. On the exposed portions of the second and third CCLs 1b and 1c, there are disposed copper or other metal layers 3a and 3b. These metal layers 3a and 3b are wire-bonded through a wire 10 to a pad 9 of the semiconductor chip 7, and therefore, the metal layers 3a and 3b are called xe2x80x9cbond fingersxe2x80x9d.
The above described printed circuit board has an advantage such that the wire bonding between the circuit board and the semiconductor chip is done within the window. Therefore, the wire bonding is not exposed to the outside, and therefore, damages are not caused by external impacts or the like.
In the printed circuit board, there are formed through-holes 11. These through holes 11 are for electrically connecting the upper layers to the lowermost layer, and the insides of the through holes 11 are electroplated with a metal. Further, a metal is electroplated on the upper face of the lowermost layer, i.e., the fourth CCL 1d, thereby forming a circuit. Accordingly, when a metal is electroplated on the inside of the through hole 11 and on the upper face of the fourth CCL 1d, the metal is also plated within the window. Particularly, the metal is plated on the bonding fingers 3a and 3b, and therefore, the circuit is liable to be short-circuited so as to cause defects.
In order to prevent the short-circuiting upon plating the bonding fingers 3a and 3b, when plating a metal on the upper face of the fourth CCL 1d to form a circuit, the window has to be blocked, so that the metal cannot intrude into the window 4.
A method for preventing the intrusion of the metal into the window is illustrated in FIG. 2. As shown in FIG. 2, a dry film 15 is spread on the fourth CCL 1d before plating the metal. Accordingly, the metal is plated in a state with the window blocked, and therefore, the bonding fingers are not plated with the metal. However, the dry film 15 has a certain mass, and therefore, in the case where the dry film having a size of 16.7 mmxc3x9716.7 mm is spread on the window, the dry film is pulled downward due to its self gravity, with the result that the dry film is ruptured. In order to prevent this rupture, if the dry film is made thicker, then the formation of fine patterns becomes impossible due to the thick thickness.
In another proposal, there is a method of attaching a copper foil on the fourth CCL 1d to block the window. In this case, however, the overall treatment cost is increased due to the complication of the copper foil treatment and the etching treatment, thereby leading to the increase of the manufacturing cost.
The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is an object of the present invention to provide a method for manufacturing a printed circuit board, in which a plurality of boards are first worked to form a slot in each of them, then an ink layer is formed within the slot, then a metal is plated, and then, the boards are subjected to a second working, thereby preventing the plating of the metal on the semiconductor installing region.
In achieving the above object, the method for manufacturing a printed circuit board according to the present invention includes the steps of: forming a circuit on each of a plurality of boards; forming a slot in each of the plurality of the boards so as to form window regions having different sizes; filling an ink into the slots to form ink layers; coupling the plurality of the boards together to form a multi-layer circuit board; forming through-holes through the multi-layer circuit board, plating a metal, and etching it; treating the ink layer with a treatment solution such as sodium hydroxide to remove the ink layer; and removing the regions of the plurality of the boards where the slots are not formed, so as to form a multi-step window in the multi-layer printed circuit board.
A semiconductor chip is installed into the multi-step window, and bonding fingers are formed on the board to be wire-bonded to the semiconductor chip.